Amidocarboxylic acids as flotation agents

ABSTRACT

Amidocarboxylic acids containing a hydrophobic group on the nitrogen are used as flotation agents. They are particularly useful as collector agents in the separation of non-sulfide minerals from their gangues.

The present invention relates to a process for enriching minerals byfroth flotation using certain amidocarboxylic acids containing ahydrophobic group. The amidocarboxylic acids are preferably used forseparation of nonsulfide minerals from their gangues.

Derivatives of sarcosine and related amidocarboxylic acids, containing ahydrophobic group on the carbon of the amido group, are well-knownflotation agents for different minerals. These types of amidocarboxylicacids are, however, comparatively expensive and they often give rise toan undesirably high degree of foam formation and the formed foam has ahigh stability.

According to the present invention it has been found that another groupof amidocarboxylic acids, namely N-acylated aminocarboxylic acids, canbe used as collector reagents for separation of minerals by frothflotation. These amidocarboxylic acids can be used at low temperaturesand in hard water and they can further be added to the pulp in pure formwithout being diluted and this without requirements on exceptionallylong conditioning times. Compared with sarcosine derivatives, such asfor example N-oleoylsarcosinate, the amidocarboxylic acids usedaccording to the invention have a substantially lower tendency to formbulky, difficult foam. The present amidocarboxylic acids do in manyinstances give a better metallurgical result than previously knownamidocarboxylic acids for flotation use and they are further veryadvantageous on a cost-performance basis.

The present invention thus relates to a process for separation ofminerals from their gangues by froth flotation in which process theflotation is carried out in the presence of an amidocarboxylic acidhaving the general formula ##STR1## wherein R is an organic, hydrophobicgroup having at least 6 carbon atoms, R₁ is hydrogen or a loweraliphatic group having 1 to 4 carbon atoms or such an aliphatic groupsubstituted with a carboxylic group and R₂ is a straight or branchedalkylene group with 1 to 6 carbon atoms, or a salt thereof.

The amidocarboxylic acids used for flotation according to the presentinvention are characteristic in that the nitrogen of the amido group issubstituted with an organic, hydrophobic group. This type ofamidocarboxylic acids, which can be classified as N-acylatedaminocarboxylic acids, is per se previously known from the publishedGerman patent application 2054649 which discloses a process for theirpreparation and their use mainly as textile additives.

In the amidocarboxylic acids of the above formula for flotation use theorganic, hydrophobic group R suitably has 6 to 22 carbon atoms and issuitably a saturated or unsaturated, straight or branched, aliphaticgroup and preferably with 8 to 18 carbon atoms. As example of groups canbe mentioned octyl, nonyl, decyl, dodecyl, tridecyl, tetradecyl,pentadecyl, heptadecyl, octadecyl and higher alkyl groups with up to 22carbon atoms, and the corresponding unsaturated groups among which assome examples can be mentioned decenyl, tridecenyl, hexadecenyl,heptadecenyl, octadecenyl, eicosenyl etc, di- and polyunsaturated groupswith at least 6 carbon atoms. The organic hydrophobic group can also bealkyl substituted aryl or aralkyl groups, cycloalkyl groups oralkylsubstituted cycloalkyl groups with at least 6 carbon atoms. As someexamples of such groups can be mentioned octylphenyl, nonylphenyl,dodecylphenyl, tridecylphenyl, nonylcyclopropyl, dodecylcyclobutyl etc.All the organic hydrophobic groups may of course contain oxygen bridgesor other inert substituents which do not negatively influence thehydrophobic properties of the groups or the affinity of the compounds tominerals.

The compounds can be used in the form of acids or as salts thereof.Salts are often used for practical reasons and hereby primarily refer tosalts of alkali metals, of ammonium or lower alkyl or hydroxyalkylamineswith 1 to 4 carbon atoms. Among the salts alkali metal salts, andparticularly sodium salts, are most often used, and this is, of course,primarily dependent on the pH in the systems. Further, the use ofmixtures of compounds according to the general formula is, of course,encompassed by the invention and such mixtures can, besides by simplemixing of derivatives before the use, be obtained in the production ofthe amidocarboxylic acids by using mixtures of the starting materials,e.g. by starting from a mixture of aminocarboxylic acids or by acylatingan aminocarboxylic acid with two or several different acylating agents.

As mentioned above, R₁ is hydrogen or a lower aliphatic group with 1 to4 carbon atoms or such a group substituted with a carboxylic group. R₂is a straight or branched alkylene group with 1 to 6 carbon atoms,preferably with 1 to 4 carbon atoms. Most preferably R₂ is a methylene-,ethylene- or an isopropylene-group.

The amidocarboxylic acids used according to the invention are preferablyprepared from an aminocarboxylic acid containing an organic hydrophobicgroup and an acylating reagent. Simple, easily available and cheap rawmaterials can thus be used throughout. The acylating reagent is a lowerorganic acid, a mono- or diacid, and suitably an anhydride or halide ofthis. Reaction of the aminocarboxylic acid with a diacid derivativeresults in compounds wherein R₁ is substituted with a carboxylic groupand wherein R₁ may contain a double bond. The raw reaction product of aprocess as described can usually be used for flotation purposes, withoutpreceding complicated purification by using only simple operations suchas washing with water and filtration, and this further improves thecost-performance relationship at the flotation.

The process for separation of minerals from their gangues comprises thesteps of forming a pulp from the raw mineral, optionally adding adepressor for the gangues and optionally conditioning the pulp, treatingthe pulp with an effective amount of the amidocarboxylic acid andseparating the minerals by froth flotation, collecting the minerals asfroth product and removing the gangues as tailings.

The amidocarboxylic acids are preferably used for separation ofnon-sulfide minerals from their gangues. As examples of non-sulfideminerals which can be upgraded according to the present invention can bementioned minerals which contain alkaline earth metals such as apatite,scheelite, wolframite, magnesite and baryte which usually are associatedwith silicates, silica and iron minerals of different kinds and fromwhich they can be separated by flotation processes. Other minerals whichcan be upgraded using the amidocarboxylic acids are hematite and otherkinds of iron minerals such as cassiterite, chromite etc.

The flotation process is carried out in a conventional manner. A pulp isformed from the raw mineral and this, after optional conditioning, issubjected to treatment with air in the presence of the collectorreagent. The minerals will hereby be hydrophobed and obtained as frothproduct while the gangues will be removed as tailings. The flotationconditions are selected in per se known manner with respect to themineral. Flotation of minerals containing alkaline earth metals isgenerally carried out under neutral or alkaline conditions at a pH above6, preferably above 8. For other minerals such as hematite andcassiterite the flotation can be carried out under more acid conditions.Conventional auxiliary chemicals can of course be used such asdepressors, dispersing agents and foam regulators, for example sodiumsilicate, dextrin and ethoxylated nonylphenols. The collector agents areoften advantageously used with fuel oils, such as diesel oil, whichenhance the hydrophobic effect of the flotation reagent. Theamidocarboxylic acids can also be used in combination with other knowncollector reagents such as fatty acids, and salts of these, and/orphosphate esters.

Mixtures of the present flotation collectors with fatty acids, i.e.carboxylic acids suitably with 6 to 24 and preferably with 14 to 22carbon atoms, are especially suitable. The ratio between amidocarboxylicacids and fatty acids in such mixtures can vary within wide limits and10 to 80 percent by weight of such a mixture can for example be made upof fatty acids.

The amount of amidocarboxylic acid is of course dependent on the type ofmineral, the desired separation effect etc and suitable amounts arereadily found by the man skilled in the art by testing in a knownmanner. Generally amounts above 40 g per ton of dry mineral are used andin most cases the amount is within the range 100 to 200 or 300 g, ormore, per ton.

The invention is further illustrated in the following examples, which,however, are not intended to limit the same. Parts and percent relate toparts by weight and percent by weight, respectively, unless otherwisestated.

EXAMPLE 1

1 kg of apatite ore containing 11.9% of P₂ O₅ and containing, besidesfluoroapatite, silicate gangue minerals and hematite, ground to size100% below 100 μm was placed in a 3.5 l Agitair flotation cell togetherwith 2.5 l of water and conditioned for 3 minutes with 0.3 g of sodiumsilicate and then for 3 minutes with 0.15 g ofN-oleic-N-formyl-3-amino-3-methylpropionic acid at a pH of 9.5. 1 dropof a foam regulator (methylisobutylcarbitol) was added and the flotationwas started. The rougher concentrate was subjected to three cleanings ina 1.5 l Agitair flotation cell without addition of any flotationreagent. The concentrate and all other products were filtered, dried andanalysed. 283 g of concentrate with a P₂ O₅ content of 37.7%,corresponding to a yield of 89.6% were obtained.

In a comparative test 0.15 g of N-oleylsarcosinate were used as acollector reagent under identical conditions and this gave 272 gconcentrate having a P₂ O₅ content of 37.1%, corresponding to a yield of84.8%.

EXAMPLE 2

1 kg of ore ground to 80% under 74 μm, containing fluorapatite (6.1% P₂O₅), hematite, some amount of magnetite and silicate gangue minerals,was conditioned in a 3.5 l Agitair flotation cell together with 2.5 lwater and 0.2 g of sodium silicate for 5 minutes. 0.22 g of a mixturecontaining 15% of oleic acid and 85% ofN-tallow-N-acetyl3-aminopropionic acid was added and the pH of the pulpwas adjusted to 9.5 by adding some drops of NaOH. After 5 minutesconditioning with this collector the flotation was started. The rougherconcentrate was cleaned three times in a 1.5 l Agitair flotation cellwithout addition of any other floatation agent. All products werefiltrated, dried and analysed. Apatite concentrate containing 36.1% P₂O₅ was obtained with recovery of 92.1%.

In a comparative test 0.22 g of a mixture of 15% oleic acid and 85%N-oleylsarcosinate was used as collector under identical conditions andthis gave apatite concentrate having a P₂ O₅ content of 35.0% to a yieldof 90.4%.

EXAMPLE 3

An ore containing 38.9 % fluorspar (CaF₂), the rest being silicategangue minerals, was ground to 80% below 70 μm. 1 kg of the ore wasplaced in a 3.5 l Agitair flotation cell together with 2.5 l water andconditioned for 6 minutes with 0.6 g of sodium silicate and 0.1 g ofethoxylated nonylphenol (6 moles of ethylenoxide). 0.3 g of a mixturecontaining 75% of oleic acid and 25% of N-oleic-N--COCH₂ CH₃--3-aminopropionic acid were then added together with some drops ofdiluted NaOH to keep the pH at 9.7. After 5 minutes conditioning theflotation was started. Rougher concentrate was cleaned twice in a 1.5 lAgitair cell without addition of any chemicals. A concentrate containing88.7% CaF₂ was obtained at 96.1% recovery.

Two comparative tests were performed with the same ore and underidentical conditions but using as collector

(a) 0.4 g oleic acid

(b) 0.3 g of a mixture containing 75% oleic acid and 25%N-oleylsarcosinate.

The test gave results as follows:

(a) concentrate containing 85.1% CaF₂, recovery 94.5%.

(b) concentrate containing 88.6% CaF₂, recovery 92.2%.

I claim:
 1. A process for the separation of apatite, scheelite andfluorspar minerals from raw materials which contain said minerals inassociation with silica, silicates or iron mineral gangues, whichprocess comprises the steps of:(1) forming a pulp of said raw mineral,(2) treating said raw material pulp with a collector reagent comprisingan amidocarboxylic acid having the general formula ##STR2## wherein R isan aliphatic group having 8 to 18 carbon atoms, R₁ is hydrogen or alower aliphatic group having 1 to 4 carbon atoms or such an aliphaticgroup substituted with a carboxylic group, and R₂ is a straight orbranched alkylene group with 1 to 4 carbon atoms, or a salt thereof, inan amount effective to form a froth, (3) carrying out froth flotation ata pH above 6 and collecting said minerals as a froth product whileremoving said gangues as tailings.
 2. A process according to claim 1wherein R₁ is hydrogen or a lower aliphatic group having 1 to 4 carbonatoms.
 3. A process according to claim 1 wherein said collector agent isN-oleic-N-formyl-3-amino-3-methylpropionic acid.
 4. A process accordingto claim 1 wherein said collector is N-tallow-N-acetyl-3-aminopropionicacid.
 5. A process according to claim 1 wherein said collector agent isN-oleic-N--COCH₂ CH₃ --3-aminopropionic acid.
 6. A process according toclaim 1 wherein R₂ is selected from the group consisting of --CH₂ --,--CH₂ --CH₂ -- and ##STR3##
 7. A process according to claim 6 wherein R₁is hydrogen or a lower aliphatic group having 1 to 4 carbon atoms.
 8. Aprocess according to claim 1 wherein said mineral is fluorapatite.
 9. Aprocess according to claim 8 wherein R₁ is hydrogen or a lower aliphaticgroup having 1 to 4 carbon atoms.
 10. A process according to claim 8wherein said collector agent isN-oleic-N-formyl-3-amino-3-methylpropionic acid.
 11. A process accordingto claim 8 wherein said collector agent isN-tallow-N-acetyl-3-aminopropionic acid.
 12. A process according toclaim 8 wherein said collector agent is N-oleic-N--COCH₂ CH₃--3-aminopropionic acid.
 13. A process according to claim 8 wherein R₂is selected from the group consisting of --CH₂ --, --CH₂ --CH₂ -- and##STR4##
 14. A process according to claim 13 wherein R₁ is hydrogen or alower aliphatic group having 1 to 4 carbon atoms.
 15. A processaccording to claim 1 wherein said mineral is fluorspar.
 16. A processaccording to claim 15 wherein R₁ is hydrogen or a lower aliphatic grouphaving 1 to 4 carbon atoms.
 17. A process according to claim 15 whereinsaid collector agent is N-oleic-N-formyl-3-amino-3-methylpropionic acid.18. A process according to claim 15 wherein said collector agent isN-tallow-N-acetyl-3-aminopropionic acid.
 19. A process according toclaim 15 wherein said collector agent is N-oleic-N--COCH₂ CH₃--3-aminopropionic acid.